1. Technical Field
The present invention relates generally to a non-volatile semiconductor memory device and, more particularly, to a high integration phase change memory device and a method of manufacturing the same.
2. Related Art
A phase change memory device is a type of non-volatile memory device that includes a phase change material, and a resistance of the phase change material is varied depending on a temperature. For example, the phase change material may be a chalcogenide (GST)-based material comprised of germanium (Ge), antimony (Sb) and tellurium (Te). The phase change material is “phase-changed” between an amorphous state and a crystalline state depending on the temperature, thereby defining a RESET state of logic level “1” and a SET state of logic level “0”.
Each of the memory cells in a phase change memory device may be comprised of a variable resistor formed of the phase change material and a switching device, for selectively driving the variable resistor, and the phase change material and the switching device are connected between a word line and a bit line. In such a phase change memory device, the word line may be formed of a junction region in a semiconductor substrate, the bit line may be formed of a wire pattern, and a diode or a MOS transistor may be used as the switching device.
Recently, areas of focus in the phase change memory include ensuring a lower reset current in the phase change memory device and embodying the phase change memory in a multi-level, for example where one cell can store plural bits. In attempts to ensure a lower reset current, reduction of a contact area between the phase change material layer and a heating electrode has been considered, for example forming the heating electrode to have as small a line width as possible. However, further reduction of the line width of the heating electrode is considered difficult, as limitations of an exposure apparatus make it difficult to reduce the line width below a resolution of a light source.
The multi-level phase change memory device is embodied by applying various write voltages. However, a resistance distribution to each of voltage bandwidths is not distinct, as such reproducibility is not good.